Tessella

There are awkward restrictions associated with Illustrator's patterns : not only are there printing issues but also you are pretty much limited to rectangular tiles.

Tessella allows you to create not only rectangular patterns but also rhombic, hexagonal, triangular ones as well. Furthermore the edges of these tiles may be curved in arbitrary ways using Escher Edit mode and then any Illustrator artwork can be associated with the tool to create beautiful designs.
What's new in this version:
Will work for AI CS2.